quaverf
Posts: 5
Joined: Thu Oct 24, 2013 10:31 pm

Bottom Solid Layers

Mon Oct 28, 2013 12:05 am

Having problems printing a smooth bottom layer on my Makergear M2. This afternoon I ran a series of trials to see if I could get a better handle on first layer issues. Creator seems to treat Solid Layers (SL) differently that Fill Layers (FL). I was printing with 1.75 mm ABS, 0.25 mm layer height, a simple rectangle plate 3D part 45X45 mm. Extrusion multiplier was set to 1.0 with Auto Extrusion Width selected.

I ran the part with a single layer skirt, 2 layer outside wall and 2 bottom solid layers. I would stop the print when the first layer completed so I could use my calipers to measure skirt height, outer wall height and SL fill height. I observed the printing activity through a 1.75 power magnification lamp. The skirts and outside walls print nice but the first SL was another story. The nozzle's proximity to the print surface (kapton tape layer) seems to force material outward excessively which caused the formation of little ridges between the beads. The skirt and outside walls were measuring around 0.21-0.23 mm height which seems right for a print layer height setting of 0.25mm. The first SL, however, measured a height anywhere from 0.45-0.52 mm. The height is caused by the ridges.

This phenomenon is the reason I was hearing/feeling the nozzle rumble over the first layer when printing the second layer and then even bumping on infill wall perimeters at higher layer counts. In short, the 0.5 mm solid first layer height (height measured at the peaks of the ridges) introduces and error that effects all subsequent layer. The nozzle is 0.25 mm closer to the print surface for each successive layer than the controller believes it to be.

I made additional trials to explore this problem further. I set Bottom Solid Layers to zero and the Infill Percentage to 60% (I actually started at 90% and stepped it down in 5% increments). With these print settings I get a 0.23-0.25 mm skirt, outer wall and first layer infill height. The first layer bead edges are fused together completely, no separation which I would consider solid. Its actually pretty impressive that the machine can print something this thin, this consistently. I then ran another trial and let the G-code continue executing until half-way through the second layer. Skirt and first infill layer measured 0.23 - 0.25 mm. Second layer infill and outer wall measured 0.49-0.51 mm; exactly what one would expect with a 0.25 mm print height setting. No ridges between the beads on the first layer; beads completely fused. However, the second layer beads are separated by about 0.5 mm with a bead width of about 0.26 mm. This makes sense as the Infill Percentage was set to 60%. So the height control is spot on with these settings. The first layer ends up being solid because the nozzles proximity to the print surface force a wider than normal aspect ratio so the bead edges close with one another.

I could leave the setting like this and probably have good luck with most parts as long as I did not want to change the infill percentage and would never need more than one solid first layer. But I will usually want at least 2 solid bottom and top layers and the infill percentage will be driven by part loading conditions. Long and short of it, I understand more about whats going on but still have an issue.

Can anyone explain whats happening in Creator when its printing Bottom Solid Layers? It seems to me that perhaps the software is flowing too much material during the formation of the Bottom Solid Layer. Biggest reason for thinking this is that the outer wall height is nearly perfect and no ridge forms between the the two beads that form the outer wall. This makes me think that Creator is extruding the Bottom Layer infill at a higher flow rate than it does when printing outer wall and normal infill. Is there a way to control the extrusion rate for solid layers?

Thanks

kaink
Posts: 20
Joined: Tue Apr 23, 2013 7:22 pm

Re: Bottom Solid Layers

Mon Oct 28, 2013 8:00 am

If you could post your fff file it would help.

I will take a shot at what's wrong though. It sounds Your nozzle is too close to the bed or your over extruding.

There is a function called "first layer height" that is supposed to be for this. It is a % and it spreads the first layer infill out to prevent this. I would try dropping it in 5% increments till it gets better or you get gaps where it turns back.

You won't see it as an issue on perimeters because its not stacking the lines together one after the other. The excess filament has somewhere to go. I bet if you went up to 3 or 4 outer walls you would get the same bead between lines. Its caused by over extruding or the nozzle to close.

quaverf
Posts: 5
Joined: Thu Oct 24, 2013 10:31 pm

Re: Bottom Solid Layers

Mon Oct 28, 2013 11:26 am

My understanding of first layer height (FLH) is that it modifies the Z position by the ammount specified in this field. In other words, "Layer Height X First Layer Offset = Commanded Z Position" for the first layer. I have validated this during my trials. With a print layer height of 0.25 mm the commanded first layer Z position as indicated in the Machine Control Panel while the G-code is running is 0.25 mm when FLH = 100%. When I set FLH = 130% the commanded first layer Z position as indicated in the Machine Control Panel while the G-code is running is 0.32 mm. BTW, the second layer commanded Z position as indicated in the Machine Control Panel while the G-code is running with FLH = 130% is 0.57 mm. In other words, all layers after the first layer continue to carry the inital FLH offset. This seems reasonable.

During my trials, I adjusted the FLH setting until I achieved a skirt and outer wall height that was close to the ideal .25 mm value. I am printing 2 passes for the skirt and outer wall and I do not see ridges forming between these beads. I see the ridge formation on the second bead when the bottom solid layer infill begins. I think this indicates that the extrusion rate is higher for the bottom solid layers than it is for skirt, perimeter wall and normal infill.

It would be nice to have an Extrusion Multiplier added to the First Layer controls.

I will run raise the number of layers used in the perimeter wall and repeat the test to see if I can get ridge formation. I dont think I will see ridges form.

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jimc
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Re: Bottom Solid Layers

Mon Oct 28, 2013 12:26 pm

on the machine control panel there is an extrusion jog dial so you can adjust on the fly. while its printing the second layer, where you feel its too much, adjust the dial down to see if it makes a difference. this way you can adjust as your printing and will be able to verify if that is the problem.

quaverf
Posts: 5
Joined: Thu Oct 24, 2013 10:31 pm

Re: Bottom Solid Layers

Mon Oct 28, 2013 1:46 pm

Good suggestion jimc. I will try that this evening.

quaverf
Posts: 5
Joined: Thu Oct 24, 2013 10:31 pm

Re: Bottom Solid Layers

Mon Oct 28, 2013 11:41 pm

test_part_annotated.JPG
Photo of Test Print
Thanks for the feedback everyone. More trials this evening. I will forego the details but in short I tried adjustment of the overlap percentage (seems to only effect how much a particular bead overlaps the perimeter shells, not the adjacent beads) and adding additional shells to the perimeter wall to see if I could coax out ridge formation. Turns out that with only two shells at the perimeter you do not get a ridge to form but if you raise that to 10 shells ridges form just like in the solid bottom layers. Conclusion: over extrusion on the first layer is not limited to the bottom solid layer but is also occurs in the perimeter band and skirt; there is simply room on the outside edge of each bead (inboard and outboard) for the material to flow in X-Y without Z displacement.

I took jimc's advise and played around with the Extrusion Override control in the Machine Control Panel. I started the print with the same settings I was using yesterday afternoon (see last post; this is Zone 1 on attached photo) and when the first bottom solid layer was about 1/3 complete I dropped the extrusion override to 56%. The remainder of the first bottom solid layer looked pretty good (see Zone 2 on attached photo). Layer 2, which is also a bottom solid layer, began to print and it was apparent that the 56% reduction in extrusion rate was not enough to close the beads (see Zone 3 of the attached photo). I changed the extrusion override back to 100% and finished off about 1/3 of layer with good results (see Zone 4 of the attached photo).

Zone 1 measures 0.51-0.53 mm thick, just as I was reporting previously. Zone 2 measures 0.24-0.26 mm think, which is what is should measure as the FFF is set for 0.25mm layer height. Zone 3 measures 0.49-0.53 mm in the area over Zone 2 which is what you would expect (sum of Zone 2 and the nominal layer height). Zone 4 measures 0.67-0.70 mm over the Zone 1 region and 0.53-0.55 mm over the Zone 2 region.

So you can see from the photo that in Zone 1 the software is over extruding for the first bottom solid layer. This is verified by the fact that when I manual override the extrusion rate to 56% the ridges disappear and the layer height comes into spec (Zone 2). Remember, this is all happening in one print run so this eliminates the effects of trial print to print variability. Also, the fact that the 56% reduction in extrusion rate is insufficient to fill the second bottom solid layer (Zone 3) but 100% extrusion rate closes it solid with almost perfect height (Zone 4) demonstrates that the second bottom solid layer extrusion rate is good.
test_part_annotated.JPG
Photo of Test Print
So while I have additional information its still not clear to me how to resolve this problem. And it is a problem. Tonight I tried to print three small parts on the bed at the same time and because of the ridge formation while working on the second layer when the nozzle passes over areas its already printed on the first layer it rips up the corners and edges because the ridge peaks are in the 0.45 - 0.50 mm height range.

I thought more about the Z end-stop position and while I have checked and double checked position and level, the actual position seems to be a mute point because you can simply use the First Layer Height (FLH) control to add an "electronic" offset to the Z axis starting position. Example, if you have the FLH set to 100% and the layer height set to 0.25 mm the commanded Z position for the first layer will be 0.25 mm BUT if you set the FLH to 125% with the same layer height setting the commanded Z potion for the first layer will be .312 mm (layer height X first layer height). I have verified this for several prints by monitoring the machine control panel position display and stopping prints in progress to measure with feeler gauges. So regardless of where I set the Z end-stop, if its reasonable, I can compensate by using the FLH. Therefore, it don't think the problem is with the Z end-stop position.

Sure seems like a lot of effort to get a part to print correctly. Has anyone experienced this kind of difficulty? Maybe I am overlooking something.

Thanks again for the help.

kaink
Posts: 20
Joined: Tue Apr 23, 2013 7:22 pm

Re: Bottom Solid Layers

Tue Oct 29, 2013 10:15 pm

Try setting the first layer height at say 80% with nothing else changed. You will see the infill for the first layer spread out slightly. It should reduce the ridges. With that and raising the z offset you should be able to get rid of it while still maintaining the first layer height. I don't think the first layer height and z-offset work exactly how they should. There are just to many variables to have it perfect. I've tried and tried to get it right by the numbers and it just doesnt work out. You have to do some tweaking by what the print is showing.

I always set my layer height to 100% and adjust the z endstop to get the right amount of squish. In the situation you are having I would just lower the bed a bit. If the fill isnt filling tightly I move it closer to the nozzle. The overall difference after the part is done has not been measurable.

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jimc
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Re: Bottom Solid Layers

Tue Oct 29, 2013 10:29 pm

kaink, i do the same and leave my layer height to 100% and adjust the endstop. once its set you rarely have to change it. on the MG forum quaverf confirmed he gets way too much material first layer so by adjusting the material jog dial down to the 56% its much better then for layer 2, 56 is not enough and has to move back to 100%. this tells me his bed is too close to the nozzle and first layer is way too thin. you can see in zone 2 how transparent it is. the z end stop should be adjusted to lower the bed little by little until it prints so each line's edge just touches the next with no spaces.

Tshulthise
Posts: 12
Joined: Wed Oct 16, 2013 5:44 pm

Re: Bottom Solid Layers

Sat Nov 09, 2013 6:22 pm

There's a lot of adjustment available via the 3 leveling screws (both for Z offset and leveling). Chances are you don't need to mess with the home switch and can just set Z offset and leveling to where you need them at the same time.

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